If you have installed Retrospect locally on the Exchange Server and Retrospect is still unable to authenticate then the following steps will NOT apply to your situation.

The following steps should only be performed if you are connecting to your Exchange server through the Retrospect Client software and you have followed Part 1 and Part 2 of the article Exchange Mailbox Backup Requirements.

On the Retrospect Backup computer go to Configure > Volumes.

Right-click on the Exchange server under Backup Clients and unlicense the Exchange client which is having login problems. Exit Retrospect.

On the Exchange client computer open the Services Control Panel.

Change the Retrospect Client Service to run as the RBU account user instead of having the client running as the default "System" account.

Start the Retrospect Client service from within the Services Control Panel on the Exchange server.

Open Retrospect on the backup computer and go to Configure > Volumes.

Right-click on the Exchange Server under backup clients and select Licensing to add the available database license to this server.

If needed, right-click on the server and select Login As and choose your authentication method.

If the above steps do not display your mailboxes and storage groups, please return to the Exchange Server and reconfigure the Retrospect Client to run as the local system account.

Retrospect should now display the Storage Groups and all mailboxes on the server.